Recently, there has been an increased interest in tailored development of polyaromatic polymers, particularly polyaromatic polymers that are electrically conductive and/or have interesting and useful optical properties. Examples of electrically conductive polymers include certain polyanilines, polythiophenes, polypyrroles, and polyphenols. These conductive polyaromatic polymers may be used in a variety of electronic devices, including electro-chromic devices, light-emitting diodes, electrostatic discharge protection, and light weight batteries. Of these polyaromatic polymers, polyanilines are the most extensively studied, due largely to superior electrical properties such as high discharge capacity.
In addition to the above-named electrical properties, the thermal and structural properties of polyphenols have long been exploited. In particular, phenol-formaldehyde resins such as novolacs and resols have found wide application as wood composites, laminates, foundry resins, abrasives, friction and molding materials, coatings and adhesives, fiber binders, and flame retardants. The use of formaldehyde in polyphenol synthesis, however, presents a significant toxicological and environmental hazard.
Despite the industrial utility of polyaromatic polymers, their synthesis remains problematic. Known difficulties in the synthesis of these polymers include inconsistent product composition, due in part to extensive branching of the polymers. In addition, many of the polyaromatic polymers are insoluble or sparingly soluble in common solvents, leading to poor processability. The use of toxic reagents, as noted above, is another undesirable feature of current synthetic methods. A search for new methods of synthesizing polyaromatic polymers has not yet yielded a commercially viable approach.
Many of the synthetic approaches to forming polyaromatic polymers use a heme-containing enzyme to catalyze the polymerization. Any such catalyst must necessarily be stable and active under acidic conditions, as acidic conditions are required in order to synthesize an electrically conductive form of a polyaromatic polymer such as polyaniline. An example of an enzyme extensively studied for aromatic molecule polymerization is horseradish peroxidase. Unfortunately, horseradish peroxidase and other peroxidases are inactive at low pH and are prohibitively expensive to use commercially. Hematin has been used to mimic the catalytic activity of horseradish peroxidase. However, despite its lower cost, hematin is a non-ideal catalyst for commercial polymerizations because of its low solubility in acidic, aqueous media. The low solubility of hematin under these conditions leads to a low rate of polymerization and poor yields. Therefore, a need exists to develop a low cost, high efficiency means of synthesizing polyaromatic polymers, which is compatible with conditions required to synthesize polymers with commercially desirable properties.